1. Field of the Invention
This invention relates to the control of automated vehicles which move around a site, such as a factory or a warehouse, in accordance with control signals generated by a computer. The invention is particularly relevant to vehicles which are controlled over radio or other remote control links and do not rely on guidance wires or tracks.
2. Description of Related Art
Our British Patent No: 2,143,395 discloses such a system in which a number of mobile trucks are controlled and guided under the overall control of a base station. The trucks are utilised to transfer material between a store area and a work position. Finished work-pieces are transferred by means of one of the trucks to a holding area for removal and utilisation as required. The base station allocates destinations to each of the trucks via a communication link, such as a radio or infra-red link.
Each vehicle is able to determine its own position relative to any location within the site. Each vehicle monitors its own position as it moves along a path to its required destination, and continuously transmits its position back to the base station, so that the base station can control the truck movements so as to avoid collisions.
Typically the storage area, the work position and the holding area may each comprise a large number of bays divided into separate sections by aisles along which the trucks must travel.
A possible way to prevent collisions between vehicles in such a system, is for the computer controlling the vehicles to store the positions of zones which only one vehicle is allowed to occupy at a time, and to ensure that if a vehicle has been instructed to move into a zone no other vehicle can approach or enter that zone. It will be apparent that such a mode of operation limits the efficiency of the system, as much time can be wasted while vehicles are waiting to move.